Howdy Pablo45, and et al.,
Wow, what a loaded question. I'm pretty sure there are quite a few more passionate responses pending. I've had the good fortune to have each. Both are fine pistols and have virtues endearing the owner to those attributes. Let me have a go at what I've found with mine in respect to your inquiry.
Duty: Both are suitable, might be a slight advantage to the G17 due to the lower overall weight. If you are hauling it about all day long those ounces can add up.
Training: Again, both are suitable, with another slight advantage to the G17 in a straightforward manual of arms. There is a consistent trigger manipulation, and no de-cocking requirement for re-holstering.
Off Duty: similar to duty, lighter might be preferable. Point of information, Clint Smith has always advocated that weapons should be comforting not necessarily comfortable... just a thought.
Concealed: Very similar, possibly a slight edge to the SIG in that the grip is not quite the same size but then again my SIG mags are 15 rounds capacity while the Glock is 17 so it is just a bit more pronounced. Arguable but only you can assess the real significance to your lifestyle.
Home defense: My choice is Glock. Capacity is it for me. Even downloading by one the Glock has the advantage. Considering this particular application, I'm probably not going to grab an extra mag so it is going down with what is in the pistol.
Plinking: Both are great. SIG has an advantage in two areas, it is slightly more accurate than the Glock. I would say that at 25 yds, it is not that much of a difference but there is a difference, we are talking a fraction of an inch average deltas. Comfort is the other advantage. Due to the additional weight and grip configuration it is more comfortable to shoot a lot of rounds through. After shooting the Glock at some of the monthly club matches, my hand is a bit fatigued from the pounding of several hundred rounds launched in just a couple of hours of fun. Shooting the SIG in a similar fashion, I've found less fatigue in my hand but it is heavier to haul about on your hip. Also there are sharp edges on the magazine base plates on the SIG mags. Glock mags are all rounded. Yes, thing you notice when you're hauling the equipment about all day long.
In summary, I have both, like both for different reasons. Glock gets shot way more than SIG, about 4 to 1 ratio. Hope this info helps. Your mileage may vary. Get out there rent, borrow, try, and or buy them. They are all good!
Cheers!